This invention relates generally to a method of making and using an asphalt composition. While the principles of the invention may be used advantageously in various applications involving asphalt, the invention is especially useful in connection with the production and application of bituminous concrete used to pave a roadway or to patch holes in existing pavement.
Bituminous concrete is a mixture of asphalt (e.g., heavy petroleum residues) with aggregate (e.g., gravel and/or sand). The prior art has recognized that the addition of sulfur to bituminous concrete produces certain advantages. For example, Kopvillem et al U.S. Pat. No. 3,738,853 states that pavements of substantially improved strength can be achieved through the use of sulfur-asphalt-aggregate mixes having high ratios of sulfur to asphalt. The patent teaches that the weight ratio of sulfur to asphalt should be at least 1:1 and preferably is from 2:1 to 5:1 or higher.
Metcalf Canadian patent No. 755,999 also discloses a sulfur-asphalt-aggregate paving composition having a weight ratio of sulfur to asphalt of at least 1:1. A more recent example of a sulfur-extended asphalt paving composition is disclosed in Schult U.S. Pat. No. 4,339,277 which teaches the addition of crushed sulfur to heated asphalt on substantially a 1:1 weight basis.
Present techniques for producing, transporting and applying asphalt are cumbersome in many respects. Asphalt is a thermoplastic material which tends to flow at ambient temperatures, the higher the temperature the greater the flow. If a large mass of ostensibly solid asphalt is broken into particles, the material initially will remain in discrete particle form but eventually will flow and re-conglomerate at ambient temperatures.
For this reason, asphalt conventionally is treated as a liquid for handling and shipping purposes. In a typical paving operation involving bituminous concrete, hot asphalt may be delivered in a tank truck from an asphalt manufacturing plant or an asphalt storage site to the site of the roadway to be paved. The hot liquid asphalt is injected into a heated pugmill at the paving site and is mixed with heated and dried aggregate to form a paving composition which is applied to the roadway.
Alternatively, a supply of bituminous concrete may be prepared by heating and drying aggregate in a rotatable drum at a central mixing plant while mixing the aggregate with hot liquid asphalt and perhaps with a small proportion of ground-up re-cycled asphalt pavement. The mix usually is trucked hot from the mixing plant to the job site and is immediately applied to the roadway. In some cases, however, the mix may be stockpiled, later transported to the paving site, re-heated and re-mixed in a heated pugmill and then applied to the roadway.
The most widely used prior methods of making an asphalt paving composition all have one significant feature in common. That is, they all require a supply of hot liquid asphalt to be available either at the road site or at the mixing plant site and they all require that the liquid asphalt be injected into and mixed with the aggregate.